Powder for accelerating projectiles for mortar systems

ABSTRACT

Powder as propulsion powder or ignition powder for accelerating projectiles for mortar systems is based on nitrocellulose and comprises a crystalline, nitramine-based energetic material at 1-30 wt % and an inorganic muzzle flash suppressor at 0.1-10 wt %. The powder is in the form of grains, and the grains on their surface optionally have an inert plasticizing additive at not more than 1 wt %. The crystalline, nitramine-based energetic material is preferably at least one compound from the group encompassing hexogen (RDX) and octogen (HMX). The inorganic muzzle flash suppressor preferably comprises at least one compound from the group encompassing potassium nitrate and potassium sulfate.

TECHNICAL FIELD

The invention relates to a powder as propulsion powder or ignition powder for accelerating projectiles for mortar systems, which is based on nitrocellulose and comprises a crystalline, nitramine-based energetic material at 1-30 wt % and an inorganic muzzle flash suppressor, the powder being present in the form of grains, and the grains on their surface optionally having an inert plasticizing additive. The invention further relates to a method for producing such a powder.

PRIOR ART

Within recent years there has been a significant shift in the area of large-caliber barrel weapons. Thus, up until the end of the Cold War, large-caliber tank and artillery systems formed the backbone of land-based units. These systems were optimized for the defence of home territory, and had a mobility limited by their great weight. In particular, weapons systems of these kinds were not transportable by air, a factor which greatly hindered rapid territorial movement.

The outbreak of the 1st Iraq conflict at the beginning of the nineteen-nineties, however, hailed a marked turn away from the existing deployment scenarios. Large-caliber barrel weapons had to be transported to the site of deployment over long distances within a short time. The 1st Iraq war therefore marked the rediscovery of mortar systems. On account of their relatively low weight, large-caliber barrel weapons of this kind can easily be transported by air in large numbers and therefore are rapidly deployable in the event of conflict. Thanks to the appearance of high-performance electronics, moreover, such as satellite navigation or guidance to target, massive improvements were possible in precision.

The recent past has shown, then, that this mobility trend is being endorsed by forces around the globe. By virtue of the great interest in mortar systems, there has been an increase in demand and, in tandem therewith, an increase in the desire for power boosting. The new mortar grenades with electronic guidance to target and with the possibility for precise spot detonation thus have a higher weight than the existing, standard grenades. This gave rise to the need for power-boosted propulsion, which compensates the effect of the greater weight on the range, or is even able to extend the range.

It has been found, moreover, that in the last twenty years, military conflicts have been located primarily in hot climate zones, such as in Iraq or in Afghanistan. The propulsion systems used hitherto largely contained nitroglycerine in order to achieve a high power potential, and were not designed for the high thermal load. It has been ascertained that important internal-ballistic data such as muzzle velocity and peak gas pressure are altered as a consequence of months-long deployment and storage in hot climate zones. The lower muzzle velocity leads to a reduction in range and therefore reduces the strike probability. In contrast, the gas pressure increases by up to 50%, posing a great safety risk on firing. The strong climatic heat exposure, furthermore, has a strong adverse effect on the chemical stability of a propulsion system, causing phenomena including the more rapid consumption of the stabilizer. Overall, therefore, conventional, nitroglycerine-containing powders, when stored in hot bunkers or below in munition crates under direct insolation, pose a safety risk, in that they may undergo a spontaneous transition to autocatalysis and may, by exploding, injure surrounding personnel and destroy buildings.

The Nitrochemie company recognized the signs of the times some while ago, and commenced development of a new generation of nitroglycerine-free high-performance powders, which showed no change in ballistic and chemical stability even in long deployments in hot climate zones—that is, their use and storage in hot climate zones posed absolutely no safety risk. This new powder generation was first developed specifically for high-power applications in medium-caliber barrel weapons, such as some subcaliber APFSDS-T munitions or full-caliber airburst munitions. Weapons systems of these kinds are typically equipped with relatively long barrels, and relatively high peak gas pressures occur on firing, typically of 3000-5000 bar.

In contrast to these, the barrels in mortar systems are much shorter and the peak gas pressures that result on firing are lower, viz. lower by 1000 bar at maximum charge, and lower correspondingly at lower charges. This means that the power is still required to undergo sufficient conversion even at a few 100 bar gas pressure. This criterion was impossible to achieve with the original nitroglycerine-free high-power formulations. Consequently there was a need for a new approach to an appropriate propulsion technology, designed for the specific conditions of mortar systems with low peak gas pressures and short weapons tubes. Likewise required of a new propulsion system of this kind is excellent chemical and ballistic stability, the propulsion system being required at the same time to exhibit the property of undergoing conversion in mortar systems with a high power yield.

DESCRIPTION OF THE INVENTION

it is an object of the invention to create a powder belonging to the technical field identified at the outset, as propulsion powder or ignition powder for accelerating projectiles for mortar systems, that exhibits excellent chemical and ballistic stability and can be converted with a high power yield.

The achievement of the object is defined by the features of claim 1. Provided in accordance with the invention is a powder, as propulsion powder or ignition powder for accelerating projectiles for mortar systems, which is based on nitrocellulose. The powder comprises a crystalline, nitramine-based energetic material at 1-30 wt % and an inorganic muzzle flash suppressor at 0.1-10 wt %. The powder is present in the form of grains. The grains may have an inert plasticizing additive on their surface. This additive is present at not more than 1 wt %, i.e, in a range of 0-1 wt %.

The grains preferably have an inert plasticizing additive on their surface at 0.01-1 wt %.

It is surprising that through the use of relatively small amounts of an inert plasticizing additive on the surface of the powder, it is possible to lower the pressure dependency at increasing temperatures. Thus it is known with regard to the propulsion powders for medium-caliber applications that with substantial amounts of an inert plasticizing additive, the pressure profile can be made flatter. Virtually no effects are achievable at less than 2 wt %. It has nevertheless emerged that this relationship does not apply to propulsion powders for mortar applications. In the case of the propulsion systems of the invention for mortar systems, a flat pressure profile is achieved with relatively small quantities of an inert plasticizing additive. If the concentration is increased, the pressure profile steepens gradually, and at a level of addition of markedly more than 1 wt %, there is a significant increase in the pressure with increasing temperature. In the preferred range of not more than 1 wt % of the inert plasticizing additive, the increase in the muzzle velocity with increasing temperature is also relatively small, and so the propulsion system is distinguished overall by a largely neutral temperature characteristic. For certain applications, moreover, no inert plasticizing additive at all is needed.

With a flat pressure profile, the powder of the invention exhibits a high degree of energetic conversion, leading to a high internal-ballistic performance capacity.

Mortar systems are understood generally to be systems which have a relatively short tube and are fired at relatively steep angles. There are mortars ranging from a caliber of 37 mm (light mortars) up to 240 mm (ultra-heavy mortars). The most important among them are the heavy mortars in calibers of 60-120 mm. A particular focus of the invention is on the mortars or the corresponding propulsion systems for systems with calibers of 60 mm, 81 mm, and 120 mm.

Furthermore, the powders of the invention may also be used as ignition powders for mortar applications. An ignition powder is mounted in the shaft of a mortar grenade and is needed to boost the impulse of the initial pyrotechnic detonation and to transmit it to the propulsion powder in the surrounding increments (horse shoes). The composition of an ignition powder is identical to the composition of a propulsion powder. The powders, however, may differ in grain dimension and in grain geometry.

Both the propulsion powder and the ignition powder are extrudable bulk powders which can be produced in a solvent process and comprise nitrocellulose as their main component. For more than a hundred years, nitrocellulose has been the major starting material for the production of monobasic, diobasic, and tribasic propellent charge powders. It is obtained by nitration of cellulose (cotton linters), is available inexpensively in large quantities, and is offered with a large spectrum of different chemicophysical properties. Nitrocellulose varies, for example, in its nitrogen content, molecular weight, or viscosity, and on the basis of these differences can be processed to the different homogeneous propellent charge powder types. The energetic content of nitrocellulose is adjusted via the nitrogen content. In monobasic formulations, nitrocellulose is the sole energetic material, implying that the energy density of nitrocellulose is relatively high by comparison with other synthetic binder polymers.

The present powders are based on nitrocellulose. The latter preferably has an average nitrogen content of 12.6%-13.25%. The further key components present in the grain matrix are a crystalline energetic material and also an inorganic muzzle flash suppressor.

The crystalline energetic material raises the energetic content of the powder and is used at a concentration in the range of 1-30 wt %. At these proportions, in a base of nitrocellulose, the average distances between the individual crystals of the crystalline energetic material are sufficiently large that predominantly the individual crystals do not make contact. As a result, on exposure to external mechanical stimuli, the shock pulse cannot be passed on from one crystal of explosive to the adjacently situated crystals. Accordingly, a primary-acting shock pulse is not multiplied and transmitted throughout the powder volume. At higher weight proportions of crystalline energetic material, in contrast, the individual crystals, considered statistically, are located too close together, and this results in a sharp rise in the vulnerability of the powder.

The inorganic muzzle flash suppressor is used at a concentration in the range of 0.1-10 wt %. Adding an inorganic muzzle flash suppressor suppresses the reaction of uncombusted gases such as hydrogen or carbon monoxide in the region of the weapon muzzle, meaning that these gases do not ignite or ignite only to a much lesser extent. Accordingly, the muzzle flash is reduced, thereby on the one hand reducing the blinding effect of the fire on the gunner and also making it more difficult for the gunner to be located.

The crystalline, nitramine-based energetic material preferably comprises at least one compound from the group encompassing hexogen (RDX) and octogen (HMX). These two compounds, of the general formula R—N—NO₂ (R=radical), have a relatively small radical R, which constitutes a small proportion of the overall molecule by comparison with the nitramine structural element. As a result, the two compounds have a relatively high energy content.

Preference is given to using RDX as crystalline energetic material. In comparison to HMX, it is more favorable and safe to produce. HMX is more expensive than RDX, but offers no particular advantages. Other nitramine compounds (e.g., NIGU, etc.) have relatively little power in comparison to RDX. For the purpose of stabilization it is also possible to use conventional active ingredients such as akardite II, for example.

With particular preference the crystalline nitramine compound has a defined average grain size. Thus, for example RDX preferably with an average grain size of 4-8 micrometers, more particularly 6 micrometers, is used. The homogeneous particle size of the crystalline energetic material permits powders to be produced that have relatively consistent chemical and ballistic properties.

Alternatively to the nitramine compounds, a nitrate ester of the general formula R—O—NO₂, for example, would also be conceivable. In comparison to nitramine compounds, though, nitrate esters are less chemically stable. It is also possible to use at least one of the following compounds as crystalline nitramine compounds: hexanitroisowurtzitane (CL-20, CAS -#14913-74-7), nitroguanidine (NIGU, NQ, CAS-#70-25-7, N-methylnitramine (tetryl, N-methyl-N,2,4,6-tetranitrobenzolamine, CAS-#479-45-8), and also nitrotriazolone (NTO, CAS#932-64-9) and triaminotrinitrobenzole (TATB, CAS#3058-38-6). All of these energetic compounds can be used individually or in combination with one another.

The proportion of the crystalline energetic material is more preferably 5-25 wt %. Especially favored are powders which have crystalline energetic materials in proportions of 10-20 wt %. At weight proportions of below 25 wt %, more particularly down to 20 wt %, the distances between the individual crystals of the energetic material are such that the vulnerability of the powder lies at a very low level. The use of an inert plasticizing additive may attenuate the vulnerability of the powder somewhat in the event of a relatively high weight proportion of the crystalline nitramine compound. As a result it is easily possible to use high proportions of the crystalline nitramine compound. in addition to its property as a crystalline energetic material, RDX also has certain stabilizing properties, which are manifested from as little as around 1 wt % and which rise only insignificantly as the proportion increases.

The inorganic muzzle flash suppressor preferably comprises at least one compound from the group of the alkali metal salts such as potassium nitrate and potassium sulfate, for example. As well as reducing muzzle flash, these compounds may also accelerate burn-off and thereby reduce the formation of residues, thereby further increasing the degree of energetic conversion.

In one particular embodiment, the inorganic muzzle flash suppressor is present in a proportion of 0.1-5 wt %.

The inert plasticizing additive which may be located on the surface of the powder grain comprises, in particular, at least one compound from the group encompassing camphor, dialkyl phthalates (preferably di-(C8-C12) phthalates or hydrogenated derivatives thereof), and dialkyldiphenylureas (preferably diethyldiphenylurea, known under the trivial name centralite II). The inert plasticizing additive may also be applied as a combination of two or more individual compounds.

The particularly preferred compound applied optionally to the surface of the powder grain is camphor.

Moreover, the surface of the powder grain is treated preferably with graphite and ethanol.

The extruded powder grains are preferably subjected to a surface treatment with ethanol and graphite. Optionally the surface is treated with an inert plasticizing additive. The inert plasticizing additive penetrates the near-surface zones of the powder grain, where it remains—that is, it is localized and is not distributed in the grain matrix. The inert plasticizing additive has a depth of penetration of a few 100 micrometers, e.g., at most 400 micrometers, preferably 100-300 micrometers. This means that at least 95 wt % of the inert plasticizing additive is present down to that depth.

The applied graphite remains preferably at the surface of the powder grain.

The effect on the properties of the powder grain of the surface treatment, i.e., of the application of ethanol and graphite and optionally of the inert plasticizing additive to the surface of the extruded powder grain, is positive. For instance, a temperature-neutral behavior and the bulk density (i.e., the amount of powder that can fit within a given container volume) are improved in particular through surface treatment with graphite and ethanol. The pressure level (i.e., the ratio of peak gas pressure to muzzle velocity) is improved particularly through the addition of the inert plasticizing additive to the surface of the extruded powder grain, although this may impair the temperature coefficient. At the same time, the grain matrix no longer necessarily includes inert compounds, and is able consequently to have the maximum possible amount of energetic compounds. The maximum effect can be achieved through a surface treatment with a combination of these substances.

In the case of powders for mortar applications, the inert plasticizing additive is more preferably present on the surface of the grain at not more than 0.1 wt %, i.e., at 0-0.1 wt %, more particularly in a range of 0.01-0.1 wt %. At these specific amounts of the inert plasticizing additive, the change in the muzzle velocity and also the pressure increase on transition to high temperatures is relatively small. With significantly larger quantities of the inert plasticizing additive, the possibility of achieving temperature-neutral behavior goes down.

The grains for propulsion preferably have a circular-cylindrical geometry with lengthwise channels in the axial direction. The number of channels is arbitrary; a grain often has one channel, or 7 or 19 channels. A propellent charge powder of this kind, also called hole powder, is consequently pourable and free-flowable, and can therefore be filled industrially into cartridges.

The ratio of length (L) to diameter (D) of the cylindrical grain typically has a value L/D=0.25-5. The length of the circular cylinder is in the range, for example, of 0.3-10 mm, and the diameter is in the range of 0.3-10 mm.

Where the invention is configured as multihole powder, preference is given to a geometry with a small pitch circle and therefore a relatively large outer wall thickness. This means that, viewed in cross section, the individual lengthwise channels are arranged more closely at the center and occupy overall a smaller pitch circle. Preferably, for example, six lengthwise channels in a 7-hole powder with a total cross section of about 3.6 mm form a pitch circle having a diameter of about 2.1 mm.

In one particular embodiment, the individual lengthwise channels of a propulsion powder have a hole diameter of 0.1-0.5 mm.

Where the powders of the invention are used as ignition powders, the grain dimensions are typically smaller than in the context of propulsion applications. Moreover, they frequently have a circular-cylindrical geometry with a central lengthwise channel. They have, for example, an outside diameter of 1.3-1.7 mm, a length of 1.5-2.0 mm, an average wall thickness of 0.6-0.8 mm, and a hole diameter of about 0.10 mm.

Alternatively the material for the powders may be present in the form of strips or may be extruded directly into a defined form suitable for barrel weapons. In this form, it is particularly suitable for large-caliber munitions. This typically includes forms for which the width is much smaller (e.g., at least 5 times or at least 10 times) than the length, and the thickness in turn is much smaller (e.g., at least 5 times or at least 10 times) than the width. Typically the thickness is, for example, 1-2 mm, the width is, for example, 10 mm or more, and the length is, for example, 100-150 mm.)

Also conceivable are what are called shaped bodies, i.e., hollow-cylindrical forms for a munition, where the sleeve is absent and/or is replaced by the shaped body arranged behind the ignition system.

The grain matrix may optionally include further additions, known per se. For stability increase it is possible, for instance, for sodium hydrogen carbonate (CAS-#: 144-55-8), calcium carbonate (CAS-#: 471-34-1), magnesium oxide (CAS-#: 1309-48-4), akardite II (CAS-#: 724-18-5), centralite I (CAS-#: 90-93-7), centralite II (CAS-#: 611-92-7), 2-nitrodiphenylamine (CAS-#: 836-30-6) and diphenylamine (CAS-#: 122-39-4) to be added. Additives such as, for instance, lime, manganese oxide, magnesium oxide (CAS-#: 1303-48-4), molybdenum trioxide (CAS-#: 1313-27-5), magnesium silicate (CAS-#: 14807-96-6), calcium carbonate (CAS-#: 471-34-1), titanium dioxide (CAS-#: 13463-67-7), tungsten trioxide (CAS-#: 1314-35-8) serve for tube relief; compounds such as phthalic esters, citric esters, or adipic esters are customary plasticizers.

Furthermore, the green grain, in other words the powder still untreated per se, in the matrix may also include further known additions, for improving the ignition behavior and for modulating the burn-off behavior, for example.

A method for producing a powder of the invention is distinguished by the fact that a solvent-containing powder dough based on nitrocellulose and on a crystalline, nitramine-based energetic material at 1-30 wt %, and on an inorganic muzzle flash suppressor is produced. Subsequently, a green grain is produced from this solvent-containing powder dough by extrusion. The solvent is removed from this green grain, and the green grain is optionally surface-treated with an inert plasticizing additive. Finally, the optionally surface-treated green grain is dried.

A powder of the invention whose binder consists primarily of nitrocellulose and which additionally comprises a crystalline, nitramine-based energetic material and an inorganic muzzle flash suppressor can be produced on existing manufacturing plants. The solid components of the formulation can be admixed with a solvent mixture, for example. The resulting solvent-moist kneading dough can be kneaded in a kneeder and then extruded in a press to the desired geometry. The extrudates can be subjected to preliminary drying and cut to the desired grain length. Then the solvent may be withdrawn from the grain. The grain may then optionally be surface-treated with an inert plasticizing additive and/or subjected to a finishing operation.

The green grain is preferably surface-treated with ethanol and graphite, i.e., graphitized. Graphitizing may be carried out as an individual method step. It is also possible, however, to apply graphite and ethanol together with the inert plasticizing additive to the green grain.

With particular preference the solvent is removed from the green grain by way of a humid air method.

The green grain obtained by extrusion comprises an inorganic muzzle flash suppressor in the grain matrix. For the removal of the solvent from the grain matrix, accordingly, the green grain ought not to be subjected to a bath process, since otherwise the water-soluble inorganic muzzle flash suppressor would be washed out of the grain matrix.

The solvent which has been used in the production process is therefore removed by means of humid air methods. In this case the solvent-moist green grain has a stream of air passed through it for 10-60 hours, this stream of air being at temperatures between 20-70° C., being saturated with water vapor, and flowing at high rates of several hundred m³ per hour. In this way the proportion of the solvent is reduced to <1%, while the water-soluble muzzle flash suppressor is not removed from the grain matrix, but instead remains therein.

After the surface-treated grain has been dried, it is preferable for finishing to take place. Finishing refers in particular to the careful drying and screening of the surface-treated grain.

Further advantageous embodiments and combinations of features of the invention will become apparent from the detailed description below and from the entirety of the patent claims.

Ways of Implementing the Invention

During the production of the green grain, various additions are added to the nitrocellulose-based powder dough; in order words, the additions are distributed uniformly within the matrix. The total amount of these additions, with the exception of the crystalline nitramine compound, is 0-10 wt % relative to the nitrocellulose, preferably 2-7 wt %. The total amount of the crystalline nitramine compound, which is typically RDX, is 0-30 wt % of the amount of nitrocellulose, preferably 0-20 wt %. The crystalline nitramine compound may have to be subjected to pre-treatment before it is added to the powder dough, in order to improve attachment to the matrix.

After the kneading of the powder dough with solvents, the green grain is extruded through a die. Subsequently the water and the solvent are removed, preferably by means of humid air drying. The green grain is subjected to a surface treatment, in which, for example, optionally, an inert plasticizing additive and preferably further additives such as graphite, for example, are applied in the presence of ethanol (impregnation+coating).

Example 1 Propulsion Powder 1 (FM 4651/21)

For the production of 520 kg of a 7-hole powder, 20 wt % of RDX, 1.2 wt % of akardite II, and 3.2 wt/o of potassium nitrate and nitrocellulose with a nitrogen content of 13.20 wt % (balance to 100 wt %) are processed to a solvent-moist kneading dough, with addition of diethyl ether and ethanol, over 70 minutes. The powder dough is subsequently pressed through a die (i.e., extruded) with a 7-hole geometry and a 5.2 mm strand cross section. The extruded strands are briefly subjected to preliminary drying in air, then cut to the desired length, and the resulting green grain is laid out evenly on fine-mesh screens. The green grain thereafter is subjected for 30 hours to a water-saturated air flow of 200 m³/h and a temperature of 30° C. and subsequently for 30 hours to a 400 m³/h air flow and a temperature of 65° C. (humid air drying). 60 kg of the green grain heated to 60° C. are subsequently admixed, in a copper polishing drum heated to 55° C., with 0.05 wt % of graphite and 1.2 litres of ethanol, which are allowed to act thereafter for one hour with continual turning. Finally, the powder is spread out on metal sheets and dried at 60° C. for 24 hours.

The resulting propulsion powder 1 with the designation FM 4651/21 has the following physical properties: 3.63 mm outside diameter, 3.61 mm length, 0.76 mm average wall thickness, and 0.20 mm hole diameter, 4251 J/g heat capacity and 1048 g/l bulk density. Chemical stability: deflagration temperature=172° C. STANAG 4582 heat flux calorimetry=44 J/g and 30.4 μW (requirement according to STANAG 4582 standard: maximum heat evolution <114 μW).

Example 2 Propulsion powder 2 (FM 4650/22)

A powder dough according to example 1 is pressed through a die (i.e., extruded) with 7-hole geometry and 4.8 mm strand cross section. The extruded strands are briefly subjected to preliminary drying in air and cut to the desired length, and the resulting green grain is subjected to humid air drying (as described in example 1). Then 60 kg of the green grain are preheated to 60° C. and transferred into a copper polishing drum which is heated at 55° C. The green grain is admixed with 0.05% graphite and with a solution of 1 wt % of camphor in 1.2 kg of ethanol, and turned continually for one hour. Finally, the powder is spread out on metal sheets and dried at 60° C. for 24 hours.

The resulting propulsion powder 2 with the designation FM 4650/22 has the following physical properties: 3.42 mm outside diameter, 3.45 mm length, 0.71 mm average wall thickness, and 0.19 mm hole diameter, 4152 J/g heat capacity and 1002 g/l bulk density. Chemical stability: deflagration temperature=172° C. STANAG 4582 heat flux calorimetry=47 J/g and 30.9 μW (requirement according to STANAG 4582 standard: maximum heat evolution <114 μW).

Comparison of Propulsion powders 1 and 2

Comparison of the pressure increase at high powder temperatures through variation in the amount of camphor

System: 120 mm pressure barrel with identical internal-ballistic characteristics to the 120 mm standard mortar M120 of the U.S. forces, particularly in relation to tube length and muzzle geometry. The projectile mass of the inert mortar grenades used was 15.5 kg. Velocity was measured by Doppler radar, and the peak gas pressure was detected piezoelectronically in the region of the muzzle. The results of the temperature firings of the two propulsion powders, with 0 wt % and 1 wt % camphor coating, carried out at powder temperatures of 21° C. and 63° C., are compiled in Tables 1 and 2 below.

TABLE 1 FM 4651/21 0 wt % camphor Charge Powder Peak gas Pressure Pressure mass temperature Velocity pressure increase change [g] [° C.] [m/s] [psi] [psi] [%] 740 21 369.0 18224 2458 13 740 63 378.5 20682

TABLE 2 FM 4650/22 1 wt % camphor Charge Powder Peak gas Pressure Pressure mass temperature Velocity pressure increase change [g] [° C.] [m/s] [psi] [psi] [%] 740 21 366.1 17494 4015 23 740 63 376.3 21509

The results in Tables 1 and 2 show that the pressure increase on transition from 21° C. to 63° C. is much less high with the propulsion powder 1 (FM 4651/21) with 0 wt % camphor than in the case of propulsion powder 2 (FM 4650/22) with 1 wt % camphor. This finding is surprising and goes against the previous experience in the medium-caliber area, according to which the increase in pressure can be lowered by an increase in the amount of camphor.

Example 3 Propulsion Powder 3 (FM 4714)

A powder dough according to example 1 is extruded through a die with 7-hole geometry and 5.1 mm strand cross section. The extruded strands are briefly subjected to preliminary drying in air and cut to the desired length, and the resulting green grain is subjected to humid air drying (as described in example 1). Then 120 kg of the green grain are preheated to 60° C. and transferred into a copper polishing drum which is heated at 55° C. The green grain is admixed with 0.05% of graphite and with a solution of 0.1 wt % of camphor in 2.4 kg of ethanol, and turned continually for one hour. Finally, the powder is spread out on metal sheets and dried at 60° C. for 24 hours.

The resulting propulsion powder 3 with the designation FM 4714 has the following physical properties: 3.58 mm outside diameter, 3.59 mm length, 0.75 mm average wall thickness, and 0.20 mm hole diameter, 4269 J/g heat capacity and 1026 g/1 bulk density. Chemical stability: deflagration temperature=172° C. STANAG 4582 heat flux calorimetry=50 J/g and 32.6 μW (requirement according to STANAG 4582 standard: maximum heat evolution <114 μW).

Comparison of Propulsion Powder 3 with a Ball Powder

Comparison of the pressure increase at high powder temperatures and the ballistic performance with nitroglycerine-containing comparison powder (GD St Marks ball powder)

System: 120 mm pressure barrel with identical internal-ballistic characteristics to the 120 mm standard mortar M120 of the U.S. forces, particularly in relation to tube length and muzzle geometry. The projectile mass of the inert mortar grenades used was 15.1 kg. Velocity was measured by Doppler radar, and the peak gas pressure was detected piezo electronically in the region of the muzzle. The results of the temperature firings of the two powder types, carried out at powder temperatures of 21° C. and 63° C., are compiled in Tables 3 and 4 below.

TABLE 3 FM 4714 0.1 wt % camphor Charge Powder Peak gas Pressure Pressure mass temperature Velocity pressure increase change [g] [° C.] [m/s] [psi] [psi] [%] 728 21 373.5 18643 2013 11 728 63 378.5 20656

TABLE 4 Comparison Powder >10 wt % Nitroglycerine Charge Powder Peak gas Pressure Pressure mass temperature Velocity pressure increase change [g] [° C.] [m/s] [psi] [psi] [%] 756 21 349.4 14659 2261 15 756 63 362.1 16920

The results in Tables 3 and 4 show that in the case of the nitroglycerine-containing comparison powder, the pressure increase on transition to 63° C. is much higher than for propulsion powder 3 (FM 4714) with 0.1 wt % camphor. Moreover, the velocity of the comparison powder at 21° C., in spite of a charge mass 28 g higher, is about 25 m/s lower, thereby critically reducing the range.

Overall, investigations on the powder of Example 3 show that this is a powder having a better performance with a low temperature dependency. Moreover, the scatter in individual measurements is much less than for the other powders, pointing to a very homogeneous powder which is therefore consistent in its performance.

Example 4 Ignition Powder 1 (FM 4483/21)

A powder dough according to example 1 is pressed through a die (i.e. extruded) with 1-hole geometry and 2.1 mm strand cross section. The extruded strands are briefly subjected to preliminary drying in air and cut to the desired length, and the resulting green grain is subjected to humid air drying (as described in example 1). Then 20 kg of the green grain are preheated to 60° C. and transferred into a copper polishing drum which is heated at 55° C. The green grain is admixed with 0.3 wt % of graphite and with 0.3 kg of ethanol, after which it is left for one hour with continual turning. Finally, the powder is spread out on metal sheets and dried at 60° C. for 24 hours.

The resulting ignition powder 1 with the designation FM 4483/21 has the following physical properties: 1.47 mm outside diameter, 1.75 mm length, 0.69 mm average wall thickness, and 0.10 mm hole diameter, 4393 J/g heat capacity and 1001 g/I bulk density. Chemical stability: deflagration temperature=172° C. STANAG 4582 heat flux calorimetry=46 J/g and 30.2 μW (requirement according to STANAG 4582 standard: maximum heat evolution <114 μW).

Example 5 Ignition Powder 2 (FM 4483/22)

A powder dough according to example 1 is pressed through a die (i.e. extruded) with 1-hole geometry and 2.1 mm strand cross section. The extruded strands are briefly subjected to preliminary drying in air and cut to the desired length, and the resulting green grain is subjected to humid air drying (as described in example 1). Then 20 kg of the green grain are preheated to 60° C. and transferred into a copper polishing drum which is heated at 55° C. The green grain is admixed with 0.3 wt % of graphite, 0.5 wt % of camphor, and 0.15 kg of ethanol, after which it is left therein for one hour with continual turning. Finally, the powder is spread out on metal sheets and dried at 60° C. for 24 hours.

The resulting ignition powder 2 with the designation FM 4483/22 has the following physical properties: 1.47 mm outside diameter, 1.75 mm length, 0.69 mm average wall thickness, and 0.10 mm hole diameter, 4343 J/g heat capacity and 995 g/I bulk density. Chemical stability: deflagration temperature=172° C. STANAG 4582 heat flux calorimetry=52 J/g and 32.4 μW (requirement according to STANAG 4582 standard: maximum heat evolution <114 μW).

Comparison of Ignition Powders 1 and 2 with a Ball Powder

Comparison of the pressure increase at high powder temperatures through variation in the amount of camphor in ignition powders 1 and 2, and comparison with imported M48 ball powder.

System: 120 mm pressure barrel with identical internal-ballistic characteristics to the 120 mm standard mortar M120 of the U.S. forces, particularly in relation to tube length and muzzle geometry. The projectile mass of the inert mortar grenades used was 14.0 kg. Velocity was measured by Doppler radar, and the peak gas pressure was detected piezo electronically in the region of the muzzle. The test was carried out with charge 4, i.e.; using four M234 standard increments. The results of the temperature firings of the two powders with camphor coatings of 0 wt % (FM4483/21) and 0.5 wt % (FM4483/22) in comparison to the imported M48 ball powder in the standard M1020 detonation cartridge, carried out at powder temperatures of 21° C. and 63° C., are compiled in Tables 5, 6, and 7 below.

TABLE 5 FM 4483/21 0 wt % camphor Charge Powder Peak gas Pressure mass temperature Velocity pressure increase Temperature [g] [° C.] [m/s] [psi] [psi] coefficient 60.9 21 320.9 13150 1708 1.13 60.9 63 328.8 14858

TABLE 6 FM 4483/22 0.5 wt % camphor Charge Powder Peak gas Pressure mass temperature Velocity pressure increase Temperature [g] [° C.] [m/s] [psi] [psi] coefficient 62.8 21 318.5 12139 1933 1.16 62.8 63 326.4 14072

TABLE 7 M48 ball powder Powder Peak gas Pressure temperature Velocity pressure increase Temperature [° C.] [m/s] [psi] [psi] coefficient 21 322.4 13650 2284 1.17 63 329.7 15934

It is apparent that the presence of 0.5 wt % of camphor in the inventive ignition powder 2 reduces the peak gas pressure at 21° C., which may be advantageous for certain applications. However, ignition powder 2 with 0.5 wt % of camphor exhibits a higher pressure increase than that without camphor. Depending on application, therefore, a precise weighing of the optimum amount of camphor must be made, in order to allow the system requirements dictated by the application to be fulfilled in the best-possible way. It is further found that in the case of the imported M48 ball powder the highest gas pressure results at 21° C. For the imported ball powder M48, the pressure increase from 21° C. to 63° C., at about 2300 psi, is much higher in comparison to the two inventive ignition powders 1 and 2.

In summary it can be stated that the nitrocellulose-containing powders of the invention, as propulsion powders or ignition powders, which comprise a crystalline, nitramine-based energetic material and an inorganic muzzle flash suppressor, and which have small amounts of an inert plasticizing additive on the surface, are suitable for accelerating projectiles for mortar systems, at the same time exhibiting a temperature-independent behavior and therefore being suitable for use independently of climatic conditions. 

1-12. (canceled)
 13. A powder, as propulsion powder or ignition powder for accelerating projectiles for mortar systems, which is based on nitrocellulose and comprises a crystalline, nitramine-based energetic material at 1-30 wt % and an inorganic muzzle flash suppressor, the powder being present in the form of grains, wherein the inorganic muzzle flash suppressor is present at 0.1-10 wt %.
 14. The powder as claimed in claim 13, wherein the grains have an inert plasticizing additive on their surface at a concentration of not more than 1 wt %.
 15. The powder as claimed in claim 14, wherein the inert plasticizing additive is present at 0.01-1 wt %.
 16. The powder as claimed in claim 13, wherein the crystalline, nitramine-based energetic material comprises at least one compound from the group encompassing hexogen (RDX) and octogen (HMX).
 17. The powder as claimed in claim 13, wherein the crystalline energetic material is present at 5-25 wt %.
 18. The powder as claimed in claim 13, wherein the inorganic muzzle flash suppressor comprises at least one compound from the group encompassing potassium nitrate and potassium sulfate.
 19. The powder as claimed in claim 13, wherein the inorganic muzzle flash suppressor is present at 0.1-5 wt %.
 20. The powder as claimed claim 14, wherein the inert plasticizing additive comprises at least one compound from the group encompassing camphor, dialkyl phthalates and dialkyldiphenylureas.
 21. The powder as claimed in claim 14, wherein the inert plasticizing additive is present at 0.01-0.1 wt %.
 22. The powder as claimed in claim 13, wherein the grains have a circular-cylindrical geometry and have lengthwise channels running in the axial direction.
 23. A method for producing a powder as propulsion powder or ignition powder as claimed in claim 13, comprising the steps of a) producing a solvent-containing powder dough based on nitrocellulose and on a crystalline, nitramine-based energetic material at 1-30 wt %, and on an inorganic muzzle flash suppressor, b) producing a green grain by extrusion of the solvent-containing powder dough, c) removal of the solvent from the green grain, d) drying of the green grain.
 24. The method as claimed in claim 23, wherein the solvent is removed from the green grain by means of humid air methods.
 25. The method as claimed in claim 23, wherein the green grain is surface treated with an inert plasticizing additive prior to the drying step.
 26. The method as claimed in claim 25, wherein the drying of the surface-treated green grain is followed by finishing.
 27. The powder as claimed in claim 14, wherein the crystalline, nitramine-based energetic material comprises at least one compound from the group encompassing hexogen (RDX) and octogen (HMX).
 28. The powder as claimed in claim 14, wherein the crystalline energetic material is present at 5-25 wt %.
 29. The powder as claimed in claim 14, wherein the inorganic muzzle flash suppressor comprises at least one compound from the group encompassing potassium nitrate and potassium sulfate.
 30. The powder as claimed in claim 14, wherein the inorganic muzzle flash suppressor is present at 0.1-5 wt %.
 31. The powder as claimed in claim 14, wherein the grains have a circular-cylindrical geometry and have lengthwise channels running in the axial direction. 